US20090071136A1

US20090071136A1 - Exhaust diffuser for an internal combustion engine

Info

Publication number: US20090071136A1
Application number: US11/901,000
Authority: US
Inventors: Kyle R. Smith
Original assignee: Mack Trucks Inc
Current assignee: Mack Trucks Inc
Priority date: 2007-09-14
Filing date: 2007-09-14
Publication date: 2009-03-19

Abstract

An exhaust outlet apparatus for an internal combustion engine comprises an exhaust conduit having a first diameter, a nozzle section mounted on an outlet end of the exhaust conduit, the nozzle section having an outlet with a second diameter less than the first diameter, an elongated tube having an inlet and an outlet, mounted with the outlet of the nozzle disposed in the inlet of the elongated tube, the elongated tube having an inlet end portion with a solid wall and an outlet end portion with an apertured wall, and, a cap disposed on the outlet end of the elongated tube and closing an axial end of the elongated tube, the cap including a cylindrical wall portion radially spaced from the elongated tube and extending longitudinally at least over the outlet end portion of elongated tube.

Description

FIELD OF THE INVENTION

The invention relates to exhaust systems for internal combustion engines, and more particularly, to an exhaust system for an internal combustion engine that mixes the exhaust gases with ambient air to reduce the temperature of the exhaust gas before exhausting to the atmosphere. The invention has advantageous application to a diesel engine in a heavy vehicle, such as a truck.

BACKGROUND AND SUMMARY OF THE INVENTION

More stringent emissions regulations on the amount of diesel particulate matter (DPM) and other gaseous constituents allowed in the exhaust gases of diesel engines has led to the use of exhaust aftertreatment devices such as diesel particulate filtration devices (DPF) and Diesel Oxidation Catalysts (DOC).
DPFs filter the particulate matter from the exhaust gases to prevent them from exiting the tailpipe. After a period of operation, the collected particulates clog the filter. The filter either needs to be replaced or removed for cleaning, which is not practical, or may be cleaned through a process known as regeneration. DPM is made up primarily of carbon, and is therefore combustible. Regeneration is a process where temperatures of the exhaust gases are made high enough to combust or oxidize the DPM within the filter. The regeneration process can cause the temperature of the exhaust gas exiting the diesel particulate filter to be well in excess of 600° C. By comparison, normal operating exhaust temperature for a diesel engine depends on the load and can range from about 100° C. at idle to about 500° C. at high load.
At highway speeds, high exhaust temperatures do not usually pose problems because the relative high air speeds tend to dissipate the heat. Exhausting the higher temperature stream can create difficulties when the vehicle is stationary or moving at low speed and is near combustible materials. A truck typically has an exhaust stack pipe rising from the chassis adjacent to the truck cab. High temperature exhaust can produce a hot spot on the truck cab or trailer, or direct hot gases to a combustible substance, such as a building structure (for example, a loading dock or in a garage) or an overhanging tree.
It is desirable to provide an arrangement and a method for lowering the temperature of engine exhaust, particularly when the engine is operated for regeneration of exhaust aftertreatment devices.
The invention provides an apparatus for incorporation at an outlet end of an engine exhaust that includes devices to dilute the exhaust flow with ambient air, which produces a flow of lower temperature, and devices to diffuse the flow into the atmosphere to avoid hot spots on the cab or adjacent structures or trees.
According the invention, an exhaust outlet apparatus for an internal combustion engine, comprises an exhaust conduit having a first diameter, a nozzle section mounted on an outlet end of the exhaust conduit, the nozzle section having an outlet with a second diameter less than the first diameter, an elongated tube having an inlet and an outlet, mounted with the outlet of the nozzle disposed in the inlet of the elongated tube, the elongated tube having an inlet end portion with a solid wall and an outlet end portion with an apertured wall, a cap disposed on the outlet end of the elongated tube and closing an axial end of the elongated tube, and a cylindrical walled body radially spaced from the elongated tube and extending longitudinally at least over the outlet end portion of elongated tube.
Exhaust gas from the exhaust conduit is accelerated by the nozzle section, which creates a low pressure area around the inlet of the elongated tube, drawing ambient air into the elongated tube. The elongated tube forms a mixing vessel for the exhaust gas in the inlet end portion.
The apertured wall portion defines a radially directed exhaust outlet of the elongated tube. Apertures in the apertured wall of the elongated tube may be any shape, including, but not limited to, circular, oblong, oval, or slotted, that produces a diffuse flow outward.
The cylindrical walled body directs the exhausted flow downward to prevent the exhaust from direct contact with trees, roofs, or other overhanging structures. In addition, the cylindrical walled body provides an additional mixing zone for the ambient air and exhaust gas. An open end of the cylindrical wall portion forms an annular outlet for diffusing the flow to atmosphere.
According to another aspect of the invention, an annular flange of baffle is disposed on the inlet end portion of the elongated tube adjacent the inlet and extending radially outward therefrom. This flange prevents gas exhausted from the cylindrical walled body from being drawn into the elongated tube.
According to yet another aspect of the invention, the exhaust outlet apparatus further comprises a cylindrical apertured element or screen element surrounding the nozzle and elongated tube and radially spaced from both. The cylindrical apertured element may be an expanded metal body to shield the elongated tube from contact with external structures or plants.
Optionally, the inlet of the elongated tube has an outwardly flared entrance to help draw ambient air into the elongated tube.
According to an alternatively embodiment, the exhaust outlet apparatus of the invention further comprises a pipe connected to the nozzle to supply air from a pressurized air source to the nozzle. The additional air may be supplied by a compressor, blower, or fan provided on the vehicle. The additional air further dilutes the exhaust gas (along with the induced air). In addition, the pressurized supplied air may be at a pressure sufficiently above the exhaust gas temperature to accelerate the gas flow in the nozzle.
The additional air may be supplied continuously, or alternatively, supplied responsive to a temperature sensed in the exhaust gas flow.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood with reference to the following detailed description read in conjunction with the appended drawings, in which:

FIG. 1 is a longitudinal section view of an exhaust apparatus in accordance with an embodiment of the invention; and,

FIG. 2 is a longitudinal section view of an exhaust apparatus in accordance with another embodiment of the invention.

DETAILED DESCRIPTION

The invention is an apparatus mountable on a vehicle exhaust pipe 10 for cooling the exhaust gases. The exhaust pipe 10 is shown with a tapered end cap 11 to reduce the exit opening and increase the velocity of gas exiting the pipe 10. The exhaust pipe 10 may be formed with the tapered end cap 11 as an integral part or an end cap may be separately formed and mounted on the end of the exhaust pipe 10.
A nozzle 20 is mounted on the end of the exhaust pipe 10 to guide the exhaust gas flow exiting the pipe into an elongated tube 30. The nozzle 20 has a tapered tip 21 to further accelerate the gas flow into the elongated tube 30. The elongated tube 30 has a diameter greater than a diameter of the nozzle 20 so that an annular entrance or inlet 31 is defined around the nozzle 20. Exhaust gas flowing from the nozzle 20 into the elongated tube 30 creates a venturi effect drawing ambient air into the elongated tube through the inlet 31. The inlet 31 of the elongated tube 30 is shown as straight walled; optionally, the inlet 31 of the elongated tube has an outwardly flared entrance.
Alternatively, the exhaust pipe 10 may be formed without the nozzle shown in FIG. 1 if the velocity of the exhaust gas exiting the pipe 10 is sufficient to draw air into the inlet 31 and the elongated tube 30.
The elongated tube 30 has a first solid-walled section 33 that provides a mixing zone for the exhaust gas and air drawn into the elongated tube. At an opposite end, the elongated tube 30 has a perforated or apertured wall section 35 that forms an outlet end portion of the elongated tube. Mixed exhaust gas and air radially exit the elongated tube 30 through the apertured wall portion 35. The apertures 37 in FIG. 1 are shown as circular holes formed in the elongated tube, but may be other shapes. FIG. 2 shows slotted apertures 38, for example. Preferably, the apertures 37 (or 38) collectively present a surface area greater than a cross sectional area of the elongated tube 30. The exiting mixed gas is diffused over the length of the apertured wall section 35. The axial end 39 of the elongated tube 30 is closed by an end cap 40.
A cylindrical walled body 50 is mounted at the end of the elongated tube 30 opposite the inlet 31 and extends longitudinally toward the exhaust pipe 10. The cylindrical walled body 50 surrounds the apertured wall portion 35 of the elongated tube 30 and is spaced therefrom to define a flow zone 53. The cylindrical walled body 50 has an axial closed end 51 which contacts the cap 40 on the elongated tube 30. The closed end 51 and cap 40 may be formed as an integral piece. Alternatively, the end cap 40 may be formed to provide an air gap 42 to insulate the end 51 of the cylindrical walled body from hot exhaust gases.
An opposite end of the cylindrical walled body 50 is open and forms an outlet 55. Flow exiting the elongated tube 30 through the apertures 37 enters the flow zone 53 and is turned from the radial direction to longitudinal to exit through the outlet 55. The flow zone 53 also provides a secondary mixing or diffusion zone for the exhaust gas and air.
Gas exits the outlet 55 of the cylindrical walled body 50 as a circular curtain flow and diffuses into the air surrounding the outlet.
A shield 60 surrounds the nozzle 20, elongated tube 30 and cylindrical walled body 50 to prevent external objects from contacting these components or coming into direct contact with the exhaust gas. The shield 60 may be conveniently formed as a cylindrical element having a mesh wall of expanded metal or other screening material.
A baffle plate 70 is mounted to the elongated tube 30 adjacent the inlet 31 to prevent exhaust gas exiting the cylindrical walled body 50 from being drawn into the elongated tube. As illustrated, the baffle plate 70 is an annular flat plate.
FIG. 2 shows an alternative embodiment of the apparatus of FIG. 1. Where the identical reference numbers are used, the components are identical to those described in connection with FIG. 1, and will not be described again.
As mentioned above, the elongated tube 30 in FIG. 2 shows an outlet end portion 35 having slotted apertures 38, as an example of an alternative hole pattern. Any suitable hole shape may be used in either embodiment.
In the embodiment of FIG. 2, an air supply pipe 80 is connected to the nozzle 20 to supply air to the exhaust gas flow in the nozzle. The air supply pipe 80 may be connected to a forced or compressed air supply, such as a fan or blower (not illustrated). Air supplied to the nozzle 20 by the air supply pipe 80 dilutes the exhaust gas. Air supplied by the air supply pipe 80 also accelerates the flow in the nozzle 20. The tapered outlet 21 of FIG. 1 may be omitted and an outlet 22 coextensive with the width of the nozzle 20 may be used as an alternative. The flow from the nozzle 20 induces air into the elongated tube 50 to mix with the exhaust flow, as described in connection with FIG. 1.
The invention has been described in terms of preferred principles, embodiments, and components; however, those skilled in the art will understand that equivalents may be substituted for what is described here without departing from the scope of the invention as defined by the appended claims.

Claims

1. An exhaust outlet apparatus for an internal combustion engine, comprising:

an exhaust conduit having a first diameter and an outlet;

an elongated tube having an inlet end and an outlet end, mounted with the outlet of the exhaust conduit disposed in the inlet end of the elongated tube to define an annular gap therebetween, the elongated tube having an inlet end portion with a solid wall and an outlet end portion with an apertured wall;

a cap disposed on the outlet end of the elongated tube and closing an axial end of the elongated tube; and,

a cylindrical walled element radially spaced from the elongated tube and extending longitudinally at least over the outlet end portion of elongated tube.

2. The exhaust outlet apparatus of claim 1, further comprising a nozzle section mounted on an outlet end of the exhaust conduit, the nozzle section having an outlet with a second diameter less than the first diameter.

3. The exhaust outlet apparatus of claim 1, further comprising an annular flange disposed on the inlet end portion of the elongated tube adjacent the inlet and extending radially outward therefrom.

4. The exhaust outlet apparatus of claim 1, further comprising a shield surrounding the nozzle and elongated tube and radially spaced from both.

5. The exhaust outlet apparatus of claim 1, wherein the shield comprises a cylindrical mesh walled body.

6. The exhaust outlet apparatus of claim 1, wherein the inlet of the elongated tube has an outwardly flared entrance.

7. The exhaust outlet apparatus of claim 1, wherein the cylindrical walled body and cap are formed as an integral piece.

8. The exhaust outlet apparatus of claim 1, wherein the cylindrical walled body is radially spaced from the apertured wall portion of the elongated tube a sufficient amount to form a mixing space.

9. The exhaust outlet apparatus of claim 1, further comprising a pipe connected to the nozzle to supply air from an air source to the nozzle.